IPTABLES REJECT Forward Policy On Edge Node

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Introduction

In this article, we will explore the IPTABLES REJECT Forward Policy on an Edge Node in a Kubernetes environment. Specifically, we will discuss the purpose of setting the Forward Policy as REJECT on an Edge Node, the implications of changing this policy to ACCEPT, and how communication takes place over the Kubernetes service layer when Calico CNI is not installed on the Edge Node.

What Happened

We have deployed a KubeEdge 1.20 on a machine with Kubernetes 1.30, using Calico CNI and Containerd CRI. Initially, the Edge Node was not ready due to the CNI plugin not being initialized or the CNI config not being uninitialized. To resolve this issue, we followed the documentation provided by KubeEdge to initialize the CNI plugin.

Once the Edge Node became ready, we used hostport to create a NGINX pod that was accessible locally from the Edge Node. However, the pod was not accessible externally due to the IPTABLES Forward Policy being set as REJECT on the KubeEdge Node. To make the pod accessible externally, we had to change the Forward Policy to ACCEPT.

What You Expected to Happen

Query 1: Purpose of Setting Forward Policy as REJECT on Edge Node

The purpose of setting the Forward Policy as REJECT on an Edge Node is to block external traffic from reaching the Node. This is a security measure to prevent unauthorized access to the Node and its resources. By setting the Forward Policy to REJECT, we can ensure that only authorized traffic is allowed to reach the Node.

Query 2: Acceptability of Changing Forward Policy to ACCEPT

Changing the Forward Policy to ACCEPT is acceptable in certain scenarios, such as when we need to access the Node externally for maintenance or troubleshooting purposes. However, it is essential to note that changing the Forward Policy to ACCEPT can compromise the security of the Node and its resources.

Query 3: Communication over Kubernetes Service Layer

When Calico CNI is not installed on the Edge Node, communication takes place over the Kubernetes service layer using the NodePort service. The NodePort service allows us to expose a service on a specific port on each Node, making it accessible from outside the cluster.

How to Reproduce It

To reproduce this issue, follow these steps:

  1. Deploy KubeEdge 1.20 on a machine with Kubernetes 1.30, using Calico CNI and Containerd CRI.
  2. Initialize the CNI plugin by following the documentation provided by KubeEdge.
  3. Create a NGINX pod using hostport and make it accessible locally from the Edge Node.
  4. Attempt to access the pod externally and observe that it is not accessible due to the IPTABLES Forward Policy being set as REJECT.
  5. Change the Forward Policy to ACCEPT to make the pod accessible externally.

Anything Else We Need to Know?

  • Kubernetes version: 1.30
  • KubeEdge version: 1.20

Conclusion

In conclusion, the IPTABLES REJECT Forward Policy on an Edge Node is a security measure to prevent unauthorized access to the Node and its resources. While changing the Forward Policy to ACCEPT is acceptable in certain scenarios, it is essential to note that it can compromise the security of the Node and its resources. Communication over the Kubernetes service layer takes place using the NodePort service when Calico CNI is not installed on the Edge Node.

Troubleshooting Tips

  • If you encounter issues with the CNI plugin not being initialized or the CNI config not being uninitialized, refer to the KubeEdge documentation for troubleshooting steps.
  • If you need to access the Node externally for maintenance or troubleshooting purposes, change the Forward Policy to ACCEPT. However, be aware of the security implications of doing so.
  • If you need to expose a service on a specific port on each Node, use the NodePort service to make it accessible from outside the cluster.

References

Q: What is the purpose of setting the Forward Policy as REJECT on an Edge Node?

A: The purpose of setting the Forward Policy as REJECT on an Edge Node is to block external traffic from reaching the Node. This is a security measure to prevent unauthorized access to the Node and its resources. By setting the Forward Policy to REJECT, we can ensure that only authorized traffic is allowed to reach the Node.

Q: Why is the Forward Policy set as REJECT by default on an Edge Node?

A: The Forward Policy is set as REJECT by default on an Edge Node to prevent unauthorized access to the Node and its resources. This is a security measure to ensure that only authorized traffic is allowed to reach the Node.

Q: Can I change the Forward Policy to ACCEPT on an Edge Node?

A: Yes, you can change the Forward Policy to ACCEPT on an Edge Node. However, be aware of the security implications of doing so. Changing the Forward Policy to ACCEPT can compromise the security of the Node and its resources.

Q: What are the security implications of changing the Forward Policy to ACCEPT?

A: Changing the Forward Policy to ACCEPT can compromise the security of the Node and its resources. This is because the Node will no longer block external traffic, making it vulnerable to unauthorized access.

Q: How can I troubleshoot issues with the CNI plugin not being initialized or the CNI config not being uninitialized?

A: To troubleshoot issues with the CNI plugin not being initialized or the CNI config not being uninitialized, refer to the KubeEdge documentation for troubleshooting steps.

Q: What is the difference between the Forward Policy and the CNI config?

A: The Forward Policy and the CNI config are two separate configurations on an Edge Node. The Forward Policy determines whether to block or allow external traffic, while the CNI config determines how the Node interacts with the CNI plugin.

Q: Can I use the NodePort service to expose a service on a specific port on each Node?

A: Yes, you can use the NodePort service to expose a service on a specific port on each Node. This allows you to access the service from outside the cluster.

Q: What are the benefits of using the NodePort service?

A: The benefits of using the NodePort service include:

  • Exposing a service on a specific port on each Node
  • Allowing access to the service from outside the cluster
  • Simplifying the process of accessing services from outside the cluster

Q: What are the limitations of using the NodePort service?

A: The limitations of using the NodePort service include:

  • Exposing the service on a specific port on each Node, which can be a security risk
  • Requiring additional configuration to access the service from outside the cluster

Q: Can I use the NodePort service with Calico CNI?

A: Yes, you can use the NodePort service with Calico CNI. However, be aware that Calico CNI may have additional requirements or configurations to use with the NodePort service.

Q: What are the best practices for configuring the Forward Policy and CNI config on an Edge Node?

A: The best practices for configuring the Forward Policy and CNI config on an Edge Node include:

  • Setting the Forward Policy to REJECT by default to prevent unauthorized access
  • Configuring the CNI config to interact with the CNI plugin correctly
  • Using the NodePort service to expose services on specific ports on each Node
  • Following the KubeEdge documentation for troubleshooting steps and configuration best practices

Conclusion

In conclusion, the IPTABLES REJECT Forward Policy on an Edge Node is a security measure to prevent unauthorized access to the Node and its resources. While changing the Forward Policy to ACCEPT is acceptable in certain scenarios, it is essential to note that it can compromise the security of the Node and its resources. Communication over the Kubernetes service layer takes place using the NodePort service when Calico CNI is not installed on the Edge Node. By following the best practices for configuring the Forward Policy and CNI config, you can ensure the security and stability of your Edge Node.